Neutron OpenVSwitch Agent service fails to start on Compute node after upgrading from OSP 5 to OSP 7

Issue

• After provisioning a Compute node via the Installer for OSP5 and upgrading it manually to OSP7 according to the procedure
  and this the neutron-openvswitch-agent service fails to start and the following messages are displayed in the /var/log/neutron/openvswitch-agent.log file:

2015-11-17 02:21:29.013 21615 INFO neutron.common.config [-] Logging enabled!
2015-11-17 02:21:29.014 21615 INFO neutron.common.config [-] /usr/bin/neutron-openvswitch-agent version 2015.1.1-7.el7ost
2015-11-17 02:21:29.016 21615 WARNING oslo_config.cfg [-] Option "rabbit_ha_queues" from group "DEFAULT" is deprecated. Use option "rabbit_ha_queues" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.016 21615 WARNING oslo_config.cfg [-] Option "rabbit_host" from group "DEFAULT" is deprecated. Use option "rabbit_host" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.016 21615 WARNING oslo_config.cfg [-] Option "rabbit_hosts" from group "DEFAULT" is deprecated. Use option "rabbit_hosts" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.016 21615 WARNING oslo_config.cfg [-] Option "rabbit_password" from group "DEFAULT" is deprecated. Use option "rabbit_password" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.016 21615 WARNING oslo_config.cfg [-] Option "rabbit_port" from group "DEFAULT" is deprecated. Use option "rabbit_port" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.017 21615 WARNING oslo_config.cfg [-] Option "rabbit_use_ssl" from group "DEFAULT" is deprecated. Use option "rabbit_use_ssl" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.017 21615 WARNING oslo_config.cfg [-] Option "rabbit_userid" from group "DEFAULT" is deprecated. Use option "rabbit_userid" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.017 21615 WARNING oslo_config.cfg [-] Option "rabbit_virtual_host" from group "DEFAULT" is deprecated. Use option "rabbit_virtual_host" from group "oslo_messaging_rabbit".
2015-11-17 02:21:29.018 21615 WARNING oslo_config.cfg [-] Option "lock_path" from group "DEFAULT" is deprecated. Use option "lock_path" from group "oslo_concurrency".
2015-11-17 02:21:29.022 21615 INFO oslo_rootwrap.client [-] Spawned new rootwrap daemon process with pid=21622
2015-11-17 02:21:29.054 21615 ERROR neutron.agent.ovsdb.impl_vsctl [-] Unable to execute ['ovs-vsctl', '--timeout=10', '--oneline', '--format=json', '--', '--may-exist', 'add-br', 'br-int'].
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl Traceback (most recent call last):
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/neutron/agent/ovsdb/impl_vsctl.py", line 63, in run_vsctl
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     log_fail_as_error=False).rstrip()
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/neutron/agent/linux/utils.py", line 111, in execute
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     execute_rootwrap_daemon(cmd, process_input, addl_env))
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/neutron/agent/linux/utils.py", line 102, in execute_rootwrap_daemon
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     return client.execute(cmd, process_input)
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/client.py", line 131, in execute
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     self._ensure_initialized()
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/client.py", line 116, in _ensure_initialized
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     self._initialize()
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/client.py", line 88, in _initialize
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     (stderr,))
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl Exception: Failed to spawn rootwrap process.
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl stderr:
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl Traceback (most recent call last):
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/bin/neutron-rootwrap-daemon", line 10, in <module>
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     sys.exit(daemon())
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/cmd.py", line 58, in daemon
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     return main(run_daemon=True)
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/cmd.py", line 95, in main
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     daemon_mod.daemon_start(config, filters)
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl   File "/usr/lib/python2.7/site-packages/oslo_rootwrap/daemon.py", line 116, in daemon_start
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl     conn = server.listener
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl UnboundLocalError: local variable 'server' referenced before assignment
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl 
2015-11-17 02:21:29.054 21615 TRACE neutron.agent.ovsdb.impl_vsctl